Numerous applications exist where it is desirable to screen for and detect the presence of small quantities of small sized particulates in large volumes of liquid. For example, detection of contaminants, disease markers, disease causing agents, or other small sized components which occur in small quantities in large volumes of liquid is desirable for the fields of health and safety, manufacturing, security and defense, and other areas in which the ability to detect the presence of minute sized particulates conveys an advantage or ability.
It is, for example, desirable to detect and quantify in foods and agricultural products analytes that may be indicative of the freshness or quality of the food, including beverages and water supplies. In routine quality control testing of foods, it is common practice to test for the presence of various contaminants, additives, degradation products, and chemical markers of microbial infestation, e.g., bacteria, bacterial endotoxins, mycotoxins, and the like. However, current methods by which such quality control testing is accomplished are typically either complex and skill-intensive analytical chemistry, molecular biology or biochemistry procedures or highly subjective and qualitative sensory evaluations, e.g., smell test, taste test, appearance, etc.
Likewise, the ability to detect contaminants in manufacturing processes, in safety and clean up processes, in the production, collection or isolation of medically useful materials, in public drinking water systems and reservoirs, waterways, bodies of water and tidal surf can provide a warning mechanism to prevent public health threats as well as the ability to identify the source and nature of such outbreaks. Moreover, protection against the dissemination of bioterrorism and chemical warfare agents, for example, is highly desirable to ensure public safety and protection.
Currently available systems have many shortcomings for meeting the challenges of detection of small particulates. For example, despite improvements in agriculture and food processing, outbreaks of disease from water-borne and food-borne pathogens still occur, including bacterial water- and food-borne diseases caused by Clostridium botulinum (botulism); Clostridium perfringens (food poisoning); Staphylococcus aureus (food poisoning); Streptococcus species (gastroenteritis); enteropathogenic Escherichia coli (gastroenteritis); Shigella dysenteriae (dysentery); Salmonella species (gastroenteritis); and Vibrio cholerae (cholera). There are also numerous water- and food-borne protozoan pathogens, such as Entamoeba histolytica, Giardia lamblia, Cryptosporidium, Microsporidia, and Cyclospora. In an attempt to avoid disease, food and water is often sampled and tested prior to distribution to determine whether it is contaminated by pathogenic microorganisms.
Numerous testing methods are available, but many common methods require that the number of organisms in a sample be expanded by promoting their reproduction prior to efforts to detect their presence. This pre-enrichment step which is performed on a specimen to increase the number of pathogenic organisms present is often time consuming; organisms are cultured in a non-selective growth medium typically for 24 hours or more. Pre-enrichment is usually necessary because pathogenic organisms may be present in very dilute amounts, thus making them difficult to detect in large volumes of liquid sample material. Second, an enrichment step may be performed in which a portion of the culture medium is transferred to an enrichment medium containing inhibitors that select for a pathogen of interest. The selected pathogen will grow further while other organisms are inhibited. Third, a measurement step is performed to discern whether pathogens of interest are present. Generally, a portion of the enrichment medium is streaked onto selective or differential agar media. The media will contain inhibitors effective against most organisms except the pathogen of interest. Indicator compounds (e.g. dyes) allow pathogen types to be visibly differentiated and thus indicate the presence and number of pathogens of interest. Exemplary alternative measurement steps are radioimmunoassay (RIA) tests, immunofluorescent assay (IFA) tests, enzyme immunoassay (EIA or ELISA) tests, DNA methods (e.g., PCR), and phage methods. For the food market, such methods are disadvantageous because they postpone distribution of fresh foodstuffs while specimens are culturing, particularly where freshness or spoilage concerns are present or it is otherwise impractical to store the food for extended periods. Furthermore, conventional methods typically only assay a small portion (≦250 g) of an agricultural crop, which may lead to analytical results that are not representative of a harvested crop as a whole. The small portion of the agricultural crop is randomly sampled across the crop population. For detecting a sporadic contamination event, this method has less than a 0.01% chance of finding the contamination.
A need exists for a convenient rapid, cost-effective, representative, and reliable method for testing for the presence of pathogens or infectious microorganisms, including during sporadic contamination events, in vegetables, fruits, nuts and other plant material intended, e.g., for animal or human consumption, and for devices and systems for carrying out such methods. A need exists for a convenient rapid, cost-effective, representative, and reliable method for concentrating an analyte which is present in small quantities in large volumes of liquid, including during sporadic contamination events, and for devices and systems for carrying out such methods.